# @Author：Kilien
# @lc app=leetcode id=225 lang=python3
# [225] Implement Stack using Queues
# time：O（1） space：O（n）
# 思路：双端队列，左进右出模拟栈

class MyStack:

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.stack = collections.deque([])
        

    def push(self, x: int) -> None:
        """
        Push element x onto stack.
        """
        self.stack.append(x)


    def pop(self) -> int:
        """
        Removes the element on top of the stack and returns that element.
        """
        for i in range(len(self.stack) - 1):
            self.stack.append(self.stack.popleft())
        return self.stack.popleft()        

    def top(self) -> int:
        """
        Get the top element.
        """
        return self.stack[-1]

    def empty(self) -> bool:
        """
        Returns whether the stack is empty.
        """
        return len(self.stack) == 0


# Your MyStack object will be instantiated and called as such:
# obj = MyStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()

